The present invention relates to a thermal transfer image-receiving sheet used in combination with a sublimation thermal transfer sheet, and more specifically it relates to a thermal transfer image-receiving sheet obtained by forming a dye receiving layer on ordinary paper using a powder composition.
Conventionally known thermal transfer recording-type image-receiving sheets employing sublimable dyes are made by coating the surface of a base (substrate) sheet such as synthetic paper or the like with a composition containing a resin having dye tingibility, and drying it to form a dye receiving layer.
Conventional dye receiving layers use solvent-type coating compositions, but in recent years the use of powdered coating compositions has been proposed as compositions for dye receiving layers (for example, Japanese Patent Laid-Open Publication Nos. 8-112974, 8-224970).
Such powdered coating compositions are prepared by melt kneading and cooling a composition comprising a resin component, whitener, static-control agent, anti-offsetting agent, etc., and then crushing it and sorting it to a suitable mean particle size. For production of the image-receiving sheet, the powdered coating composition is adhered to the surface of the sheet serving as the base such as ordinary paper by a method such as the electrostatic powder coating method, and then heating, pressurizing, or heating and pressurizing it for fixing to form the dye receiving layer. The image-receiving sheet features a simpler production process and layer structure.
However, forming dye receiving layers using powdered coating compositions is different from production of image-receiving sheets by formation of dye receiving layers on the surface of synthetic paper or the like using solvent-type coating compositions, and several problems have become apparent.
Specifically, because powdered coating compositions are coated onto the base surface in a powdered state, spaces are present between the powder particles, whereby a completely continuous coating is not formed even after fixing by heating and pressurization, and fine gaps and spaces are therefore present. In addition, when powdered coatings are coated onto the surfaces of porous bases such as ordinary paper, the coating compositions penetrate into the gaps in the pulp. The coated powdered coating further penetrates to the interior of the base due to the heating and pressurization for fixing.
Thus, when forming a dye receiving layer by coating a powder composition on the surface of ordinary paper, the actual thickness of the dye receiving layer formed is not a constant thickness corresponding to the coating amount even if the coating amount is kept constant as with conventional coating. Thus the dye receiving layer is strongly influenced by surface irregularities, etc. arising from the form of the pulp of the ordinary paper, so that it has not been possible to consistently obtain adequate printing quality and printing sensitivity.
It is therefore an object of the present invention according to its first aspect to provide a thermal transfer image-receiving sheet with a dye receiving layer formed from a powder composition, the thermal transfer image-receiving sheet having a dye receiving layer which gives high-quality transfer images and has satisfactory printing sensitivity, as well as a production process by which the thermal transfer image-receiving sheet can be consistently obtained.
According to the prior art described above, generation of roughness on the surface of the dye receiving layers resulting in lower image quality has been a problem when powder compositions are used to form dye receiving layers on the surface of ordinary paper which is used as the base.
It is therefore an object of the present invention according to its second aspect to provide a thermal transfer image-receiving sheet with a dye receiving layer formed from a powder composition, which thermal transfer image-receiving sheet can give satisfactory transfer images without generating roughness on the dye receiving layer surface when ordinary paper is used as the base.